1. Technical Field
The present invention relates to the chemical mechanical polishing or planarizing of semiconductor and similar-type substrates. More specifically, the substrate is non-rigidly held by a tooling head and is polished by contact with an abrasive material in a controlled, chemically active environment.
2. Discussion of the Related Art
U.S. Pat. No. 5,759,918 to Hoshizaki et al is directed to a method for chemical mechanical polishing. Hoshizaki teaches a polishing pattern which xe2x80x9cmaintains substantially constant instantaneous relative velocity between the polishing medium and all points on the substrate to be polished.xe2x80x9d Such a design is however problematic.
The xe2x80x9cconstant instantaneous relative velocityxe2x80x9d taught in Hoshizaki will compound any flaws in the polishing substrate. For example, if unwanted debris contaminates the polishing medium as the medium is installed on the tool, then the exact same portion of the substrate will be harmed by the contamination, over and over again during the polishing operation.
This problem could be addressed by periodically indexing a web of polishing medium. However, indexing merely creates a polishing medium having a continuum of oldest to newest polishing medium When such an indexed polishing medium is used in accordance with the Hoshizaki patent, the xe2x80x9csubstantially constant instantaneous relative velocity between the polishing medium and all points on the substrate to be polishedxe2x80x9d causes certain portions of the substrate to be polished by the newer portions of the polishing medium and other portions of the substrate to be polished by the older portions of the polishing medium.
Hence, indexing the polishing medium and practicing the polishing methods of Hoshizaki will result in a non-uniform, final polished product. However, without indexing, the polishing methods of Hoshizaki will cause any defect in the polishing medium to disproportionately harm only a particular portion of the substrate, thereby also causing non-uniform polishing.
Applicant has found a way to overcome the non-uniformity problems inherent in the teachings of Hoshizaki, while providing excellent planarization, reliability, ease of use, and low cost.
The present invention is directed to a method of chemical mechanical polishing and planarization of electronic substrates, including memory disks, blank silicon (or other semiconductor material) wafers, and/or patterned wafers (e.g., wafers supporting an integrated circuit or a precursor thereto). In a preferred embodiment, the substrate or wafer is held in a wafer carrier and the wafer is contacted by a polishing medium. The wafer is able to move relative to the wafer carrier during polishing or in other words is non-fixedly engaged by the carrier.
In this preferred embodiment, the wafer will define an initial orientation with respect to the carrier immediately prior to polishing. During polishing, the carrier and the polishing medium are moved relative to each other in a polishing pattern. The polishing pattern preferably defines a series of curves, and optionally also includes straight line movement between one or more curves. The polishing pattern maintains a substantially constant instantaneous relative velocity between the polishing medium and all points on the wafer. Also during polishing, the wafer moves relative to the carrier in a continuous or discontinuous fashion so as to change the initial orientation of the wafer in the carrier while the wafer substantially follows the movement of the carrier. This movement of the wafer relative to the carrier changes the substantially constant instantaneous relative velocity between at least one point on the wafer and the polishing medium by at least 0.01%, and preferably by at least 1% to 10%.
In one embodiment, the polishing pattern is conducted by moving the polishing medium and keeping the wafer carrier stationary. Alternatively, the polishing medium can be kept stationary and the wafer carrier moved in accordance with the polishing pattern.
According to the invention, the wafer may be rotated in the carrier on an axis extending perpendicular to the polishing medium In one embodiment, the wafer can angularly float in the carrier, and the wafer is induced to rotate in the carrier by frictional forces between the wafer and the polishing medium which are greater than frictional forces between the wafer and the carrier. In another embodiment, the wafer is coupled to the carrier to prevent float, and the carrier is mechanically driven to effect positive rotation of the wafer with respect to the polishing medium.
In an alternative embodiment, rather than measuring the instantaneous relative velocity between the wafer""s initial position and the polishing medium, the instantaneous relative velocity is measured between the wafer during polishing and the polishing medium If the instantaneous relative velocity between the wafer (during polishing) is measured relative to the polishing medium, the relative velocity cannot match 100%, i.e., is not substantially constant. The velocity of one relative to the other must be different by at least about 0.1, 0.2, or 0.5 percent, but no more than about 1, 3, 5 or 10 percent.
In one embodiment, the polishing movements are controlled with control circuitry. Preferred control circuitry provides precise movement of the carrier relative to the polishing medium in accordance with the present invention.